Many equipment and technical advances have been made since the early 1980's in the field of whitewater recreational sports. At the same time the average kayak paddler is attempting more challenging rivers and tries to execute more technical whitewater acrobatic maneuvers, than ever before. The average paddler may still lack many of the basic kayak handling skills that allow for greater control of a kayak. The present invention in particular focuses on providing kayak features which improve its performance in regards to a particular technique known as the flat spin.
In general, flat spins are performed by stroking the water with a paddle, with a circular motion which results in the kayak spinning on the surface of the water. Several factors influence this technique. One such factor being the length of the hull at the waterline.
The shorter the waterline of the hull, the easier the spin. Therefore, according to common knowledge, improved handling in a flat spin can be achieved either by shortening the overall length of the hull or by adding a rocker to the hull. A kayak hull with a rocker is one which has upswept ends. This effectively shortens the waterline without shortening the length of the hull itself. There are disadvantages in both cases. The most common being, a significant reduction in speed and increased draft, because the craft sits lower in the water with the chines thus being presented to rocks and water currents.
At certain speeds, which vary from one hull to another, a kayak will begin to plane. Planing is a condition in which the motion of the hull is more influenced by surface effect between the outer skin and the surface of the water than by the fluid flow characteristics to displacement conditions. Planing hulls can plane at much lower speeds. Given that kayaks are man powered, a kayak with a planing hull design is desirable in executing flat spin maneuvers.
At planing conditions the hull rises out of the water, therefore reducing the risk of presenting the sideboard to oncoming rocks and water currents while effectively reducing the length of the hull at the waterline and thus allowing the hull to spin better.
However, planing hulls also tend to `wander about` when planing. This is due to the fact that at planing conditions there is only a very small portion of the hull in the water thereby reducing translational stability or, in terms encountered in the art, there is very little "hull in the water" to provide a "bite" to keep the craft on course.
At low speeds, when the hull is barely planing, the craft tends to be unpredictable. This is due to fluctuations in power output generated by inconstant speeds and river current surges. An inconstant speed leads to the oscillating motion of the kayak alternating dramatically between planing and displacement conditions. The handling of the craft under these conditions in a flat spin maneuver is rough and unpredictable.
It is known in the art, to provide surfing canoes and whitewater kayaks with features that enhance their translational stability under planing conditions. These designs incorporate longitudinal grooves and bevels into the hull that run parallel with the longitudinal axis of the kayak from bow to stern or a portion thereof. These features sustain translational stability, solving some of the problems mentioned above, but because of the longitudinal disposition of these features which restrict the direction of travel of the water according to the disposition of these grooves, the craft's ability to spin is inhibited.